This invention relates to a coordinate plotter equipped with an automatic punching device which forms, through a sheet laid on a table of the coordinate plotter, one or more positioning holes with predetermined distances apart from an origin of the coordinate plotter so as to hold the sheet on the predetermined position, a method for feeding sheets such as photosensitive sheets, peel-off films or Kent paper sheets onto the table, and an apparatus for practicing the method.
In conventional laying-out and block copying works making use of coordinate plotters, a plurality of positioning holes were formed by a puncher at predetermined positions of end portions of a mask for multiple exposure or a base sheet for patching and layout work and an original picture sheet so that the mask or base sheet can be brought into exact registration with a desired position of the original picture sheet, the thus-punched mask or base sheet was stored in an unprocessed sheet tray of a sheet feeding and ejecting device, a pinned bar corresponding to the puncher was provided detachably at a predetermined position of an end portion of the drafting table of the coordinate plotter, and the mask or base sheet was positioned on the table by the pins of the pinned bar so as to coincide the relative positions of the mask or base sheet and the original picture sheet.
It is however considerably difficult as a matter of fact to automatically fit unprocessed sheets, through which positioning holes have been formed in advance, on a pinned bar of a coordinate plotter, because the fitting tolerance between the positioning holes and pins is designed to be extremely small so as to assure the accuracy of positioning of the sheet. It is hence necessary to position the sheets exactly when fitting the sheets on the pins, and the feeder must thus be constructed with an extremely high level of accuracy. Accordingly, it is impractical to fit such unprocessed sheets on such a pinned bar.
As a matter of fact, the positioning and removal of each sheet is thus effected manually. However, it is obviously desirous to effect the replacement work of sheets without need for operators if one wants to impart some automatic controlling function to a coordinate plotter with a view toward achieving unattended operation.
Regarding such automatic sheet replacement means, the present assignee has already proposed to use means disclosed in the specification of Japanese Patent Application No. 102369/1982 entitled "AUTOMATIC FEEDING AND EJECTING DEVICE FOR SHEETS". Practically speaking, it is however impossible to accomplish accurate positioning of such sheets as mentioned above.
By the way, the principal objective of formation of positioning holes through sheets is to facilitate the positioning of the sheets in subsequent steps, for example, to superpose and align a multi-exposing mask, fabricated by a coordinate plotter, with a picture film or to determine the relative position of a patching and laying-out base sheet for each color-separated printing plate. It is generally unnecessary to position an unprocessed sheet exactly when drawing a picture on the unprocessed sheet by means of a coordinate plotter.
Positioning holes may be successfully used also for positioning the sheet in subsequent steps if the positioning holes are formed with predetermined positional relationship relative to a completed picture pattern in a drawing work making use of a coordinate plotter. For this purpose, it is only necessary to form the positioning holes while holding the sheet in place on a table of the coordinate plotter when drawing the desired picture pattern at a predetermined position of the sheet laid on the table.
On the other hand, the present assignee has already filed a Japanese patent application on an apparatus for automatically feeding and ejecting sheets to and from a coordinate plotter or the like (Japanese Patent Application No. 102369/1982). However, there has recently been proposed a coordinate plotter in which a puncher is provided on a fixed frame adapted to guide a table so that the puncher can form holes through a sheet supplied to the table in order to facilitate the positioning of the sheet in the subsequent step. If an automatic sheet feeding and ejecting apparatus, such as that mentioned above, is combined as is with the above-proposed coordinate plotter, the resulting system will encounter such a problem as will be mentioned next. Namely, a suction device moves in the feeding and ejecting apparatus so as to suck up a sheet for its conveyance. This movement of the suction device will however be interfered by the puncher, whereby failing to convey the sheet to a desired position.
The above problem has become more serious in the case of such a puncher-equipped coordinate plotter as described above, because the puncher-equipped coordinate plotter is required to feed each sheet over an extra distance compared with previous coordinate plotters having no punchers so as to insert the sheet into the puncher.
It may be contemplated to suck each sheet at a point somewhat apart from its leading edge in order to avoid the above-mentioned problem. If the sucked point of the sheet is too far from its leading edge, the leading edge portion of the sheet will hang down and insertion of the sheet into the puncher will thus be rendered more difficult.
As a countermeasure against the above-mentioned problem, it may also be contemplated to provide additional mechanical insertion means. This will however lead to another drawback that the coordinate plotter will be rendered more complex and more costly.